An electrochemical system is a system that either derives electrical energy from chemical reactions, or facilitates chemical reactions through the introduction of electrical energy. An electrochemical system generally includes a cathode, an anode, and an electrolyte, and is typically complex with multiple scales from nanometers to meters. Examples of these systems include batteries and fuel cells. On-line characterization of batteries or fuel cells in vehicles is difficult, due to very rough noisy environments.
On-line characterization of such electrochemical systems is desirable in many applications, which include real-time evaluation of in-flight batteries on a satellite or aviation vehicle, and dynamic diagnostics of traction batteries for electric and hybrid-electric vehicles. In many battery-powered systems, the efficiency of batteries can be greatly enhanced by intelligent management of the electrochemical energy storage system. Management is only possible with proper diagnosis of the battery states.
Accurate estimation of battery capacity is critically important for battery life and health assessment. Especially for on-board applications, the battery state estimations also rely on the capacity information for more accurate estimates of battery states. Not knowing the true capacity of a battery may lead to errors in the battery state calculations, thus adversely affecting the accuracy and robustness of the battery state estimations. Conventionally, the capacity of a cell can be estimated by fully discharging it and integrating the measured current (coulomb counting method). However, for online applications, this is rarely an option. Moreover, good accuracy of the battery capacity estimation is a prerequisite for battery health prognosis, because the battery health estimation relies on the estimates of battery capacity fade over the life of the cell to project its future life.
What are needed are methods and systems that can be implemented on-board and used in real-time, to provide reliable capacity estimation even as a battery ages. It is desirable to provide a method for on-line monitoring of the battery capacity without a reference electrode present, and without the requirement of a complete discharge in order to determine the capacity, which is not suitable for on-line diagnostics. Preferably, such methods and systems are applicable to various metal-ion (e.g., Li-ion) secondary battery systems with different material chemistries.